Thanks, fransknorge. I had not known about double-clicking the forum icon to mark the forum as read.

Javascript is off and Firefox is much more responsive. The objective measure of "much more responsive" is that the spinning circle on the left of a new tab is quickly replaced by the small FlyerTalk icon. (When the new tab contains a thread, the first unread post is displayed at the top of the window pane after the FlyerTalk icon appears, which means if scroll to read, the displayed text jumps back when the tab has finished loading. This disrupts my reading, which led to this discussion.) I hope that was clear.

However, Activity Monitor still says Firefox is using 90-120% of the CPU cycles if MyFlyerTalk or any FlyerTalk forum tab is open. (It drops to about 80% if only thread tabs are open.) I'm curious about what is going on, but much less concerned now that Firefox seems more responsive.

Thanks again!